Ossification of posterior longitudinal ligament (OPLL) is a hyperostotic disease of the spine associated with myelopathy which is occurred by an anterior compression to the spinal cord. OPLL was first reported by Key GA in 1838, and was previously considered specific to east Asian people, especially Japanese. However, now OPLL is recognized as a subtype of diffuse idiopathic skeletal hyperosteosis, which is detected in Europe and the United States. We discuss the etiology and natural history of OPLL in this review.